[dev.ssa] cmd/compile: use Copy instead of ConvNop

The existing backend simply elides OCONVNOP.
There's no reason for us to do any differently.
Rather than insert ConvNops and then rewrite them
away, stop creating them in the first place.

Change-Id: I4bcbe2229fcebd189ae18df24f2c612feb6e215e
Reviewed-on: https://go-review.googlesource.com/12810Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/gc/ssa.go

@@ -1005,8 +1005,51 @@ func (s *state) expr(n *Node) *ssa.Value {
 			return nil
 		}
 	case OCONVNOP:
+		to := n.Type
+		from := n.Left.Type
+		if to.Etype == TFUNC {
+			s.Unimplementedf("CONVNOP closure %v -> %v", n.Type, n.Left.Type)
+			return nil
+		}
+
+		// Assume everything will work out, so set up our return value.
+		// Anything interesting that happens from here is a fatal.
 		x := s.expr(n.Left)
-		return s.newValue1(ssa.OpConvNop, n.Type, x)
+		v := s.newValue1(ssa.OpCopy, to, x) // ensure that v has the right type
+
+		// named <--> unnamed type or typed <--> untyped const
+		if from.Etype == to.Etype {
+			return v
+		}
+		// unsafe.Pointer <--> *T
+		if to.Etype == TUNSAFEPTR && from.IsPtr() || from.Etype == TUNSAFEPTR && to.IsPtr() {
+			return v
+		}
+
+		dowidth(from)
+		dowidth(to)
+		if from.Width != to.Width {
+			s.Fatalf("CONVNOP width mismatch %v (%d) -> %v (%d)\n", from, from.Width, to, to.Width)
+			return nil
+		}
+		if etypesign(from.Etype) != etypesign(to.Etype) {
+			s.Fatalf("CONVNOP sign mismatch %v (%s) -> %v (%s)\n", from, Econv(int(from.Etype), 0), to, Econv(int(to.Etype), 0))
+			return nil
+		}
+
+		if flag_race != 0 {
+			s.Unimplementedf("questionable CONVNOP from race detector %v -> %v\n", from, to)
+			return nil
+		}
+
+		if etypesign(from.Etype) == 0 {
+			s.Fatalf("CONVNOP unrecognized non-integer %v -> %v\n", from, to)
+			return nil
+		}
+
+		// integer, same width, same sign
+		return v
+
 	case OCONV:
 		x := s.expr(n.Left)
 		ft := n.Left.Type // from type
@@ -1014,7 +1057,7 @@ func (s *state) expr(n *Node) *ssa.Value {
 		if ft.IsInteger() && tt.IsInteger() {
 			var op ssa.Op
 			if tt.Size() == ft.Size() {
-				op = ssa.OpConvNop
+				op = ssa.OpCopy
 			} else if tt.Size() < ft.Size() {
 				// truncation
 				switch 10*ft.Size() + tt.Size() {
@@ -1310,6 +1353,18 @@ func (s *state) zeroVal(t *Type) *ssa.Value {
 	return nil
 }
 
+// etypesign returns the signed-ness of e, for integer/pointer etypes.
+// -1 means signed, +1 means unsigned, 0 means non-integer/non-pointer.
+func etypesign(e uint8) int8 {
+	switch e {
+	case TINT8, TINT16, TINT32, TINT64, TINT:
+		return -1
+	case TUINT8, TUINT16, TUINT32, TUINT64, TUINT, TUINTPTR, TUNSAFEPTR:
+		return +1
+	}
+	return 0
+}
+
 // addr converts the address of the expression n to SSA, adds it to s and returns the SSA result.
 // The value that the returned Value represents is guaranteed to be non-nil.
 func (s *state) addr(n *Node) *ssa.Value {

src/cmd/compile/internal/ssa/gen/AMD64.rules

@@ -78,10 +78,6 @@
 (Trunc64to16 x) -> (Copy x)
 (Trunc64to32 x) -> (Copy x)
 
-(ConvNop <t> x) && t == x.Type -> (Copy x)
-(ConvNop <t> x) && t.IsInteger() && x.Type.IsInteger() && t.Size() == x.Type.Size() -> (Copy x)
-// TODO: other ConvNops are safe?  Maybe all of them?
-
 // Lowering shifts
 // Unsigned shifts need to return 0 if shift amount is >= width of shifted value.
 //   result = (arg << shift) & (shift >= argbits ? 0 : 0xffffffffffffffff)

src/cmd/compile/internal/ssa/gen/genericOps.go

@@ -203,7 +203,7 @@ var genericOps = []opData{
 	{name: "ClosureCall"}, // arg0=code pointer, arg1=context ptr, arg2=memory.  Returns memory.
 	{name: "StaticCall"},  // call function aux.(*gc.Sym), arg0=memory.  Returns memory.
 
-	// Conversions: signed extensions, zero (unsigned) extensions, truncations, and no-op (type only)
+	// Conversions: signed extensions, zero (unsigned) extensions, truncations
 	{name: "SignExt8to16"},
 	{name: "SignExt8to32"},
 	{name: "SignExt8to64"},
@@ -223,8 +223,6 @@ var genericOps = []opData{
 	{name: "Trunc64to16"},
 	{name: "Trunc64to32"},
 
-	{name: "ConvNop"},
-
 	// Automatically inserted safety checks
 	{name: "IsNonNil"},   // arg0 != nil
 	{name: "IsInBounds"}, // 0 <= arg0 < arg1

src/cmd/compile/internal/ssa/opGen.go

@@ -357,7 +357,6 @@ const (
 	OpTrunc64to8
 	OpTrunc64to16
 	OpTrunc64to32
-	OpConvNop
 	OpIsNonNil
 	OpIsInBounds
 	OpArrayIndex
@@ -2722,10 +2721,6 @@ var opcodeTable = [...]opInfo{
 		name:    "Trunc64to32",
 		generic: true,
 	},
-	{
-		name:    "ConvNop",
-		generic: true,
-	},
 	{
 		name:    "IsNonNil",
 		generic: true,

src/cmd/compile/internal/ssa/regalloc.go

@@ -167,7 +167,7 @@ func regalloc(f *Func) {
 			//   - definition of v.  c will be identical to v but will live in
 			//     a register.  v will be modified into a spill of c.
 			regspec := opcodeTable[v.Op].reg
-			if v.Op == OpCopy || v.Op == OpConvNop {
+			if v.Op == OpCopy {
 				// TODO: make this less of a hack
 				regspec = opcodeTable[OpAMD64ADDQconst].reg
 			}

src/cmd/compile/internal/ssa/rewriteAMD64.go

@@ -1294,45 +1294,6 @@ func rewriteValueAMD64(v *Value, config *Config) bool {
 		goto endc395c0a53eeccf597e225a07b53047d1
 	endc395c0a53eeccf597e225a07b53047d1:
 		;
-	case OpConvNop:
-		// match: (ConvNop <t> x)
-		// cond: t == x.Type
-		// result: (Copy x)
-		{
-			t := v.Type
-			x := v.Args[0]
-			if !(t == x.Type) {
-				goto end6c588ed8aedc7dca8c06b4ada77e3ddd
-			}
-			v.Op = OpCopy
-			v.AuxInt = 0
-			v.Aux = nil
-			v.resetArgs()
-			v.AddArg(x)
-			return true
-		}
-		goto end6c588ed8aedc7dca8c06b4ada77e3ddd
-	end6c588ed8aedc7dca8c06b4ada77e3ddd:
-		;
-		// match: (ConvNop <t> x)
-		// cond: t.IsInteger() && x.Type.IsInteger() && t.Size() == x.Type.Size()
-		// result: (Copy x)
-		{
-			t := v.Type
-			x := v.Args[0]
-			if !(t.IsInteger() && x.Type.IsInteger() && t.Size() == x.Type.Size()) {
-				goto endfb3563f9df3468ad8123dbaa962cdbf7
-			}
-			v.Op = OpCopy
-			v.AuxInt = 0
-			v.Aux = nil
-			v.resetArgs()
-			v.AddArg(x)
-			return true
-		}
-		goto endfb3563f9df3468ad8123dbaa962cdbf7
-	endfb3563f9df3468ad8123dbaa962cdbf7:
-		;
 	case OpEq16:
 		// match: (Eq16 x y)
 		// cond: